(1) Field of the Invention
The present invention generally relates to fuel injection systems for internal combustion engines. More particularly, the invention relates to an improved fuel injector for supplying fuel to an internal combustion engine and methods of controlling the improved fuel injection nozzle. Accordingly, the general objects of the present invention are to provide novel and improved methods and apparatus of such character.
(2) Description of the Related Art
Fuel injection nozzles for supplying fuel to internal combustion engines are well known in the art. Such injectors typically employ an injector body which is affixed to an internal combustion engine such that a nozzle end thereof extends into an engine cylinder. The injector body defines an interior cavity which is fluidly connected with a fuel supply and includes a needle valve which cooperates with the injector body to selectively permit fluid received from the fuel supply to pass through the interior cavity of the injector body and into the engine cylinder. Since most internal combustion engines employ a plurality of cylinders, it is common to employ one or more of such injectors with each engine. Recent developments have focused on supplying fuel to these multiple injectors from a common fuel supply rail which is maintained at very high-pressure, e.g., about 20,000 psi or about 1,380 bars.
One of this type of common rail injector is shown in FIG. 1, during the non-injection phase of the injection cycle. The injector 10 of FIG. 1 employs a hydraulic force imbalance scheme wherein a power piston 12 employs a hydraulic force imbalance scheme wherein a power piston 12 disposed at one end of a needle valve assembly 14 cooperates with other components to control the net system forces acting upon the needle valve 14. In the design shown, a control chamber 16 which lies adjacent one end of the power piston 12 contains a volume of high-pressure fuel during the non-injection phase of the injection cycle. The force of this high-pressure fuel acts downwardly on the power piston 12 to overcome the opposed upward force of the high-pressure fuel acting on annular surface 17 and to thereby urge an opposite end 20 of the needle valve 14 into sealing engagement with apertured nozzle 21 of an injector body 24. In this non-injection phase of operation, the fuel supplied to the injector 10 via inlet 11, is not permitted to pass into the engine cylinder. However, for the injection phase, the pressure within the control chamber 16 can be relieved by energizing a solenoid actuator 33 to move a valve 26 and open a spill path 28 from the control chamber 16 to low-pressure fuel region 52 thereby decreasing the pressure in the control chamber 16. When the pressure within the control chamber 16 drops to a predetermined level, based on the geometry of various injector components, the needle valve 14 moves upwardly to permit fuel to flow through the apertured nozzle 21 of the injector body 24 and into the engine cylinder. De-energizing the solenoid actuator 33 closes the fuel spill path 28. The pressure within the control chamber 16 then increases until it overcomes the upward force acting on the surface 17 and the needle valve 14 is again urged into its initial position. With the fuel injection cycle thus completed, it can be repeated as desired.
Fuel injectors of the type discussed above suffer from a number of deficiencies which tend to limit overall performance. Injector performance can deviate from the ideal due to a wide variety of performance variables and conditions. For example, limitations on manufacturing tolerances can result in the production of injectors which deviate from nominal design specifications. Moreover, changes in fuel viscosity can have a substantial impact on injector performance even in perfectly manufactured injectors. A difference in fuel viscosity can, for example, result from the use of different fuel types and grades. Additionally, ambient environmental conditions such as temperature can cause further fuel viscosity variations. Another factor impacting injector performance characteristics is physical wear and deterioration of injector components occurring over the field-life of the injector. Finally, changes in the electrical characteristics of the actuators employed with such injectors can result in still further deviations from ideal performance. These and other factors all contribute to injector performance characteristics which can deviate measurably from those originally intended.
In order to compensate for such deviations, microprocessor-based fuel injector control systems have been developed. Such control systems more precisely regulate the fuel injection timing and/or quantity by improving the electrical control of electrical actuators used with such injectors. One example of such a control system is described in U.S. Pat. No. 5,103,792 dated Apr. 14, 1992 and entitled "Processor Based Fuel Injection Control System", the contents of which are hereby incorporated by reference. While injection control systems such as those described in U.S. Pat. No. 5,103,792 have resulted in marked improvements in injector performance, further improvements are still possible. In particular, the more directly and rapidly a dedicated sensor can detect the moment at which injection begins (BOI), the more precisely the control system can regulate timing and quantity of the fuel passing through an injector.